The prior art methodology for the preparation of carbon fibers employs high heat and extended periods of time to obtain the final product. The final carbon fiber product in prior art methodology is often a flawed product that contains weak spots and micro-bubbles. This is because present processes cannot control rapid increase in heat due to heating above the fusion point of the fiber. The only prior art strategy to handle this problem is to increase the temperature of the PAN (polyacrylonitrile) fiber to just below the fusion point of the copolymer fiber, and then to SLOWLY heat the fiber for an extended period of time; thus avoiding “burn out” of the fiber. The fiber employed in prior art processes does not begin to cross-link until late in the heating cycle (near the fusion point of the fiber). “Burn out” of the fiber occurs when the temperature of the fiber reaches the fusion point. The internal temperature of the fiber shoots up to 400 degrees C. and above. The result is that the fiber is destroyed. Thus, the prior art methods depend on slowing down the heating process, and then slowly raising the temperature over the next couple of hours.
A prior art process for preparing carbon fiber includes the use of three to four monomers. The monomers can be: acrylonitrile (90-98% by wt.), itaconic acid (2-10% by weight), ethyl acrylate (2-5% by wt.), and vinyl sulfonic acid (1-3% by weight). In a first step, the four monomers are polymerized as by a precipitation polymerization process in the presence of a Redox catalyst. The resultant polyacrylonitrile copolymer is then wet spun into fibers. The fibers have a density of about 1.2 grams/cc. The PAN (polyacrylonitrile) fibers are then removed to a first oxidation zone. The fibers are SLOWLY heated in an energy intensive process for a time of about 3-4 hours. The process must be carefully monitored to prevent runaway heating from the interior of the fibers.
PANOX (oxidized polyacrylonitrile) fibers are withdrawn from the first oxidation zone. The density of the PANOX fibers is about 1.4 grams/cc. The PANOX fibers can be used in areas of technology such as sporting equipment and the like. If pure carbon fibers are desired, the PANOX fibers are removed to a second oxidation zone which is a high temperature carbonization unit. Temperatures in the carbonization unit are from 1000-2000 degrees C., or even higher. All atoms other than carbon are vaporized away from the fibers to obtain a pure carbon fiber.
U.S. Pat. No. 5,462,799 discloses the preparation of a carbon fiber wherein a precursor PAN-fiber is oxidized, carbonized and if necessary graphitized to make the carbon fiber of specified surface oxygen concentration, specified surface concentration of hydroxyl groups and specified surface concentration of carboxyl groups.
U.S. Pat. No. 5,281,477 discloses the preparation of a carbon fiber having high tenacity and high modulus of elasticity. Pretreated fibers are passed through a first carbonization zone, a second carbonization zone and a third carbonization zone.
The problems of the current methodology for preparation of carbon fiber are, among others, as follows: (1) failure to recognize the fact that amidines are the true catalysts in the preparation of carbon fiber; (2) failure to recognize that metal ions “poison” the fiber at every step of the process; and must be substantially eliminated, (3) failure to recognize that the first oxidation step can be performed in a substantially reduced time frame, thus saving a considerable amount of energy.
Therefore there is a need for a process of preparing superior carbon fiber that overcomes the drawbacks of the prior art.